Voltage-Gated Sodium Channel Phosphorylation at Ser571 Regulates Late Current, Arrhythmia, and Cardiac Function In Vivo

Abstract

Background— Voltage-gated Na + channels (Na v ) are essential for myocyte membrane excitability and cardiac function. Na v current ( I Na ) is a large-amplitude, short-duration spike generated by rapid channel activation followed immediately by inactivation. However, even under normal conditions, a small late component of I Na ( I Na,L ) persists because of incomplete/failed inactivation of a subpopulation of channels. Notably, I Na,L is directly linked with both congenital and acquired disease states. The multifunctional Ca 2+ /calmodulin-dependent kinase II (CaMKII) has been identified as an important activator of I Na,L in disease. Several potential CaMKII phosphorylation sites have been discovered, including Ser571 in the Na v 1.5 DI-DII linker, but the molecular mechanism underlying CaMKII-dependent regulation of I Na,L in vivo remains unknown. Methods and Results— To determine the in vivo role of Ser571, 2 Scn5a knock-in mouse models were generated expressing either: (1) Na v 1.5 with a phosphomimetic mutation at Ser571 (S571E), or (2) Na v 1.5 with the phosphorylation site ablated (S571A). Electrophysiology studies revealed that Ser571 regulates I Na,L but not other channel properties previously linked to CaMKII. Ser571-mediated increases in I Na,L promote abnormal repolarization and intracellular Ca 2+ handling and increase susceptibility to arrhythmia at the cellular and animal level. Importantly, Ser571 is required for maladaptive remodeling and arrhythmias in response to pressure overload. Conclusions— Our data provide the first in vivo evidence for the molecular mechanism underlying CaMKII activation of the pathogenic I Na,L . Relevant for improved rational design of potential therapies, our findings demonstrate that Ser571-dependent regulation of Na v 1.5 specifically tunes I Na,L without altering critical physiological components of the current.